Timing circuit



United States Patent O 3,543,054 TIMING CIRCUIT Elliott G. Schrader, Huntington Beach, Calif., asslgnor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Filed Mar. 27, 1968, Ser. No. 716,656 Int. Cl. H031: 1/14 US. Cl. 307265 5 Claims ABSTRACT OF THE DISCLOSURE A circuit in which pulse A is always produced before pulse B, and pulse B will always terminate before pulse A terminates, the circuit serving as a safety device. A timing signal turns over a flip-flop circuit, the output of which produces not only pulse A but also a trigger signal for an adjustable width monostable multivibrator. The monostable multivibrator initiates pulse B, which due to natural delay, is subsequent to pulse A. When the monostable multivibrator switches back to its rest state, it terminates pulse B and resets the flip-flop which terminates pulse A.

STATEMENT OF GOVERNMENT INTEREST The invention defined herein may be manufactured and used by or for the Government of the United States of America for Governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION The present invention relates to a timing circuit and more specifically to a timing circuit in which a second pulse cannot be produced before a first pulse is produced, and termination of the second pulse terminates the first pulse.

Prior art radar systems which utilized a prepulsing pulse to initiate transmitter RF drive experienced difiiculty in selecting a method for timing and developing the required prepulsing pulse. The nature of the radar required that the prepulsing pulse lie, timewise, inside the mixer protection pulse.

The standard method considered first for timing and developing the required pulses consisted of two adjustable time delays and two adjustable-width multivibrators connected as two parallel channels both fed by a single trigger input. One of the channels led to the mixer protection switching circuits while the other was connected to the transmitter RF prepulsing circuits. This arrangement had many inherent disadvantages, the most important of which were that two adjustable delays were required and also two width adjustments were required. Also, it was possible to adjust the circuit in such a manner as to damage the mixer.

An alternate method used by prior art was to employ an adjustable delay line feeding into a dual multivibrator, one output of which went to the mixer protection switching circuits while the other output was connected to the transmitter RF prepulsing circuits. This arrangement provides some improvement in that one delay adjustment and one width adjustment were eliminated and that it was no longer possible to adjust the circuit in such a manner as to damage the mixer.

SUMMARY OF THE INVENTION The present invention provides considerable improve ment over these prior art devices in that the required trigger is derived from the leading edge of the transmitter pulse thereby eliminating any delay circuits, only one input trigger line is required, only one width determining circuit is required, and it is not possible to misadjust the circuit so as to permit the transmitter output to be applied to an unprotected mixer.

An object of the present invention is the provision of a timing circuit.

Another object is the provision of a transmitter RF drive prepulsing circuit in which only one input trigger line is required.

Still another object is the provision of a transmitter RF drive prepulsing circuit in which only one width determining circuit is required.

Still another object is the provision of a transmitter RF drive prepulsing circuit in which it is not possible to misadjust the circuit so as to permit transmitter output into an unprotected mixer.

Yet another object is the provision of a timing circuit in which pulse A is always produced before pulse B, and pulse B will always terminate before pulse A terminates, the circuit serving as a safety device.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. 1 shows a block diagram of the invention and FIG. 2 shows a schematic diagram of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1 there is shown an input terminal 11 which receives trigger signals, these signals being passed on by line 12 to a bistable flip-flop circuit 13. Flipfiop circuit 13 produces a first output pulse on line 14 which may, for example, connect with mixer protection switching circuits (not shown). Also connected to flipflop 13 is another line 15 which leads to an adjustable width multivibrator 16, this multivibrator producing a second output pulse on line 17 which may go to some utilization circuit, such as to a transmitter RF prepulsing circuit, for example. A feedback, or reset line 18, joins multivibrator 16 with flip-flop 13 and is used to reset the flip-flop once the pulse has been produced, as will be shown hereinafter.

In the schematic circuit of FIG. 2 there is shown the input terminal 11 with its lead 12 connecting to flip-flop 13. Connected in lead 12 there is a coupling condenser 19 and a bypass resistor 21 leading to ground. Connected to the junction of capacitor 19 and resistor 21 is the anode of a diode rectifier 22, the base of which leads to the base connection of an NPN transistor, which may be of the type 2N914. The emitter of transistor 23 is connected to ground while its collector leads through a series resistance 24 to a source of positive potential. Also connected to the collector is the first output lead 14 which, as has been stated previously, may lead to mixer switching circuits. The second stage of the flip-flop 13 consists of another NPN transistor 25, this stage likewise having its emitter connected to ground and its collector connected through a series resistance 26 to a source of positive potential. Cross connected between the base of transistor 23 and the collector of transistor 25 there is an RC circuit consisting of a capacitor 27 in parallel with a resistor 28. Also cross connected between the base of transistor 25 and the collector of transistor 23 there is another RC circuit consisting of a capacitor 30 connected in parallel with a resistor 31. A resistor 32 connecting the source of potential with the base of transistor 25 completes the circuitry for flip-flop 13.

Connected to the collector of transistor 25 is the line 15, labelled here as a trigger line, which serves to apply an output of flip-flop 13 to the input of multivibrator 16, the line 15 being connected to the base of an NPN transistor 33. Series connected in the line 15 before it joins the base of transistor 33 there is a resistor 34 and a coupling capacitor 35. Transmitter 33 has its emitter connected to ground and its collector connected through a series resistance 36 to a source of positive potential. Also connected to the source of positive potential is a resistor 37 the inner end of which is connected to the anode of a diode rectifier 38, the rectifier 38 being connected to the collector of transistor 33. The other half of multivibrator 16 is made up of another NPN transistor 40 having its emitter connected to ground and its collector connected by means of a series resistance 41 to a source of positive potential. A bypass resistor 42 also connects the base of transistor 40 to ground. Cross connected between the base of transistor 33 and the collector of transistor 40 there is an RC circuit consisting of capacitor 43 connected in parallel with a resistance 44. From the junction of resistor 37 and the anode of diode 38 there is a connection consisting of a capacitor 45 in series with a rectifier 46, the anode of 46 being connected to condenser 45 and the cathode being connected to the base of transistor 40. In order to provide a means for adjusting the width of the output pulse of multivibrator 16 there is provided a series circuit connected to the anode of diode 46 and the source of positive potential, the circuit consisting of an accurate, low tolerance, resistance 47 connected to a potentiometer 48 which in turn is connected to a choke coil 50. The second output of the system as produced on line 17, and which may go to some utilization circuit such as a transmitter RF prepulsing circuit, is provided at the collector of transistor 40.

In order to provide a means for resetting flip-flop 13 once multivibrator 16 has cut ofi? there is provided a reset line 18 which joins the collector of transistor 33 with the base of transistor 25, the line 18 having a coupling condenser 51 therein to provide proper isolation.

Turning now to the operation of the invention it will be seen that the circuit is straightforward. When a trigger pulse is received at terminal 11 it is applied through line .12, capacitor 19, and rectifier 22 to the base of transistor 23. This causes the flip-flop 13 to change state so that transistor 23 now conducts, providing an output at its collector and on line 14 so as to afford protection to the mixer switching circuits. At the same time an output pulse is also produced on line 15 which is applied to the base of transistor 33 and is used to trigger the monostable multivibrator 16 causing the beginning of the transmitter pulse which is provided on output line 17, leading to the transmitter RF prepulsing circuits. The natural delay in this triggering process, as caused by the RC circuit 43, 44 insures that the transmitter output will not occur until after the mixer is protected. The width of the transmitter RF pulse is controlled by the adjustable width feature of the monostable vibrator as provided by resistance 47, potentiometer 48, and choke coil 50.

When the monostable multivibrator 16 switches back to its resting state, that is when transistor 40 cuts off and transistor 33 conducts, it terminates the transmitter RF pulse on line 17. When the multivibrator switches and transistor 33 conducts there is an output pulse produced as its collector which is applied through coupling capacitor 51 to reset line 18, this pulse being applied to the base of transistor 25 of the flip-flop 13, thereby causing transistor 25 to reset to its initial state by means of transistor 25 conducting and transistor 23 cutting off. When transistor 23 cuts oil it terminates the mixer protection on line 14; however, the natural delay in this reset process insures that the transmitter Will be off before the mixer protection is removed.

From the above description of the structure and opera-' tion of the invention it is obvious that the present device offers considerable improvement over prior art protection circuits. It can be seen that pulse A (mixer protection) will always be produced before pulse B (transmitter pulsing), and pulse B will always terminate before pulse A terminates, these circuits serving as a safety device. In accomplishing these ends the invention requires only one input trigger line and only one width determining circuit is required. Furthermore, it is not possible to misadjust the circuit in such a way as to permit transmitter output with an unprotected mixer.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood, that within the scope of the appended claims, the invention may be practiced otherwise that as specifically described.

What is claimed is:

1. A timing circuit comprising:

means for applying a trigger signal to the bistable flipa first output for utilization by a first external circuit;

a multivibrator;

means for connecting the flip-flop and the multivibrator;

a second output for utilization by a second external circuit; and

reset means from the multivibrator back to the flip-flop,

whereby the second output always occurs subsequent to the first output and the second output terminates prior to termination of the first output.

2. The circuit of claim 1 wherein the first output is produced by the bistable flip-flop.

3. The circuit of claim 2 wherein the second output is produced by the multivibrator.

4. The circuit of claim 3 wherein the multivibrator has means for adjusting the width of the second output.

5. The circuit of claim 4 wherein the multivibrator is a monostable multivibrator.

References Cited UNITED STATES PATENTS 3,048,714 8/ 1962 Poole 307265 X 3,049,625 8/1962 Brockman 307292 X 3,317,843 5/1967 Emmons 307273 X 3,349,255 10/1967 McAvoy 307292 3,461,321 8/1969 Greene 307273 DONALD D. FORRER, Primary Examiner R. C. WOODBRIDGE, Assistant Examiner US. Cl. X.R. 

